All are at graduate level, all based in London. Frankly your experience with any of them will be broadly identical for the next 2 years, so go for the one which pays best. And living in London you'll want/need the cash.

Plus, when you come to move on in the next 18 months to 2 years, having Accenture on your CV will make life easier, it's recognised as a tech services firm. KPMG you'll spend time explaining what they do in cyber security before talking about yourself, BAE you'll spend time explaining what they do in cyber security, why you went there instead of a more recognised consulting firm (such as Accenture) and then about yourself.